Disk array control device with two different internal connection systems

ABSTRACT

A disk array control device includes a plurality of channel interface (IF) units, a plurality of disk IF units, a cache memory unit, and a shared memory unit. The connection system between the plurality of channel IF units and plurality of disk IF units and the cache memory unit is different from the connection system between the plurality of channel IF units and plurality of disk IF units and the shared memory unit. In the invention, the plurality of channel IF units and the plurality of disk IF units are connected via a selector to the cache memory unit whereas the plurality of channel IF units and the plurality of disk IF units are directly connected to the shared memory unit with no selectors.

This is a continuation of application Ser. No. 09/358,374, filed Jul.21, 1999, now U.S. Pat. No. 6,385,681.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to control devices of disk array devicesfor storing data in a plurality of magnetic disk devices.

2. Description of the Related Art

In view of the fact that the input/output (I/O) performance orthroughput of a disk subsystem (referred to as “subsystem” hereinafter)is less by approximately three to four orders of magnitude than the I/Othroughput of main memories of computers with semiconductor memorydevices as their storage media, attempts have conventionally been madeto reduce this difference. Namely, attempts have been made to improvethe I/O throughput of the subsystem. One prior known approach toimproving the subsystem's I/O throughput is to use a system, called“disk array,” for constituting the subsystem from a plurality ofmagnetic disk devices such as fixed or “hard” disk drives (HDD5)adaptable for use in storing data in such plurality of HDDs.

FIG. 2 shows an arrangement of one prior art disk array. This includes aplurality of channel interface (IF) units 11 for execution of datatransmission between a host computer 50 and a disk array control device2, a plurality of disk IF units 12 for execution of data transferbetween HDDs 20 and the disk array control unit 2, a cache memory unit14 for temporality storing data of HDDs 20, and a shared memory unit 15for storing control information as to the disk array controller 2 (forexample, information concerning data transfer control between thechannel and disk IF units 11, 12 and the cache memory unit 14), whereinthe cache memory unit 14 and shared memory unit 15 are arranged so thatthese are accessible from all of the channel IF units 11 and disk IFunits 12. With this disk array, the channel and disk IF units 11 anddisk IF units 12 are connected to the shared memory unit 15 on aone-to-one basis; similarly, the channel IF units 11 and disk IF units12 are connected one by one to the cache memory unit 14. This connectionform is called the star connection.

The channel IF unit 11 has an interface for connection with the hostcomputer 50 and also a microprocessor (not shown) for controllinginput/output with respect to the host computer 50. The disk IF unit 12has an interface for connection to the HDDs 20 and a microprocessor (notshown) for controlling input/output relative to HDDs 20. The disk IFunits 12 also executes RAID functions.

FIG. 3 shows a configuration of another prior art disk array. Itincludes a plurality of channel IF units 11 for execution of datatransfer between a host computer 50 and a disk array controller 3, aplurality of disk IF units 12 for execution of data transfer betweenHDDs 20 and the disk array controller 3, a cache memory unit 14 fortemporality storing data of HDDs 20, and a shared memory unit 15 forstoring control information as to the disk array controller 3 (e.g.information concerning data transfer control between the channel anddisk IF units 11, 12 and the cache memory unit 14), wherein each ofchannel IF units 11 and disk IF units 12 is connected by a shared bus130 to the shared memory unit 15 whereas each channel and disk IF unit11, 12 is connected by a shared bus 131 to the cache memory unit 14.Such connection form is called the shared bus connection.

To render scalable the disk array's architectures, it is required thatthe disk IF units be additionally provided in accordance with therequired number of disks being connected to the disk control devicewhile increasingly providing the channel IF units within the disk arraycontroller as per the required number of channels associated with a hostcomputer(s). However, with the disk array controller of the shared busconnection form shown in FIG. 3, because it is impossible to change ormodify the transfer ability of the once-mounted shared bus in accordancewith the add-in provision of the channel IF units and disk IF units, itremains difficult to flexibly accommodate such add-in extendedreconfiguration of the channel IF units and disk IF units.

With the shared bus connection form shown in FIG. 3, in the case ofemploying high-performance processors as the microprocessors provided inthe channel IF units and those in the disk IF units, the shared bus'stransfer ability becomes a bottle neck when compared to the performanceof these processors, which leads to difficulty in keeping up with thegrowth of high-speed computer processor technology.

Further, in the shared bus connection form shown in FIG. 3, in caseswhere disturbance or operation failures occur at any one of theplurality of channel IF units (or a plurality of disk IF units) asconnected to the shared bus, it is difficult to specify which one of thechannel IF units (or, disk IF units) suffers from such trouble.

On the contrary, in the disk array controller of the star connectionform shown in FIG. 2, it is possible to increase the internal pathperformance or throughput in a way proportional to the number of accesspaths being connected to either the shared memory unit or cache memoryunit, which in turn makes it possible to increase the throughput ofinternal paths in accordance with the add-in reconfiguration of thechannel and disk IF units or alternatively with the performance ofprocessors used. In addition, as the one-to-one (star) connection isused between the channel IF and disk IF units and the cache memory unitor between the channel and disk IF units and the shared memory unit, itis easy to specify a channel IF unit (or disk IF unit) at which anoperation failure was occurred.

In the disk array controller of the star connection form, increasing thenumber of those channel IF units or disk IF units as built therein wouldresult in an increase in number of access paths between the channel anddisk IF units and the cache memory unit and between the channel and diskIF units and the shared memory unit. Additionally, the throughput calledfor disk array control devices tends to further increase due toemployment of high-speed channels, such as fiber channel, for connectionbetween host computers and disk array controllers; in order to satisfythis need for improvement of throughput, it should be required toincrease the number of access paths between the channel and disk IFunits and the cache memory unit and between the former and the sharedmemory unit to thereby improve the internal path throughput.

However, the data amount of a single data segment or datum to be storedin the cache memory is much greater than the data amount of a singlecontrol information item being stored in the shared memory. One exampleis that in a disk control device as connected to a mainframe, a singledatum being stored in the cache memory is several kilobytes (KB) or moreor less (for example, 2 KB) whereas one control information item storedin the shared memory is several bytes or therearound (e.g. 4 bytes).Another example is that in disk control devices as connected to hostcomputers of open architectures, a single datum as stored in the cachememory is several tens of byte (e.g. 64 bytes) whereas a single controlinformation item stored in the shared memory is about several bytes(e.g. 4 bytes). Accordingly, the amount of data to be transferredbetween the channel and disk IF units and the cache memory unit isextremely greater than the data mount being transferred between thechannel and disk IF units and the shared memory unit, which leads to aneed for letting the data width of an access path between the channeland disk IF units and the cache memory unit be wider than the data widthof an access path between the channel and disk IF units and the sharedmemory unit. For instance, the access path of the former is constitutedfrom a 16-bit width bus whereas the latter is from a 4-bit width bus.For this reason, increasing the line number of access paths between thechannel and disk IF units and the cache memory unit would result increation of a problem of shortage of the pin number of an LSI(s) of thecache memory unit for connection of the access paths thereof.Additionally, in order to shorten the response time to the host computerof a disk array control device, it is also required to minimize a timetaken to give access to the control information as stored in the sharedmemory unit.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a diskarray control device having high throughput and short response timewhich takes into consideration characteristics of data to be stored in acache memory and shared memory and of access characteristics to thesememories, along with a subsystem using the same.

It is another an object of the invention is to provide a disk arraycontrol device with access paths having high throughput between channelIF units and disk IF units and a cache memory unit and also with accesspaths having high throughput between such channel and disk IF units anda shared memory and with a short access time, and also a subsystem usingthe disk array controller.

To attain the foregoing objects, a disk array control device is providedwhich includes a plurality of channel interface units having aninterface with a host computer, a plurality of disk interface unitshaving an interface with a magnetic disk device, a cache memory unit fortemporarily storing therein data being read/written with respect to saidmagnetic disk device, and a shared memory unit for storage of controlinformation as to data transmission between the channel interface unitsand disk interface units and said cache memory unit, wherein eachchannel interface unit executes data transfer between the interface withthe host computer and the cache memory unit whereas each disk interfaceunit executes data transfer between the interface with the magnetic diskdevice and the cache memory unit, characterized in that the connectionform between said plurality of channel interface units and saidplurality of disk interface units and said cache memory unit isdifferent from the connection form between said plurality of channelinterface units and said plurality of disk interface units and saidshared memory unit.

Preferably, the plurality of channel interface units and said pluralityof disk interface units are connected via a selector unit to said cachememory unit, while said plurality of channel interlace units and saidplurality of disk interface units are directly connected via no selectorunit to said shared memory unit respectively.

Also preferably, the plurality of channel interface units and saidplurality of disk interface units are connected via one or more selectorunits to the cache memory unit, and the plurality of channel interfaceunits and the plurality of disk interface units as well as said sharedmemory unit are connected to a common bus.

Also preferably, the plurality of channel interface units and saidplurality of disk interface units are connected to said cache memoryunit via an interconnection network using one or more switches whereassaid plurality of channel interface units and said plurality of diskinterface units are directly connected to said shared memory unitrespectively.

These and other objects, features and advantages of the invention willbe apparent from the following more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a disk array controldevice in accordance with the present invention.

FIG. 2 is a diagram showing a configuration of one prior art disk arraycontroller.

FIG. 3 is a diagram showing a configuration of another prior art diskarray controller.

FIG. 4 is a diagram showing a configuration of a CM access control unitwithin the disk array controller in accordance with this invention.

FIG. 5 is a diagram showing a configuration of an SM access control unitwithin the disk array controller in accordance with the invention.

FIG. 6 is a diagram showing a configuration of a selector unit in thedisk array controller in accordance with the invention.

FIG. 7 is a diagram showing a configuration of a cache memory unit inthe disk array controller in accordance with the invention.

FIG. 8 is a diagram showing a configuration of a shared memory unit inthe disk array controller in accordance with the invention.

FIG. 9 is a diagram showing a procedure during writing data into thecache memory unit.

FIG. 10 is a diagram showing a procedure during writing data into theshared memory unit.

FIG. 11 is a diagram showing a procedure during doubly writing data intotwo cache memory units duplicated.

FIG. 12 is a diagram showing a procedure when copying data from onecache memory unit into another cache memory unit.

FIG. 13 is a diagram showing a procedure during doubly writing data intotwo shared memory units duplicated.

FIG. 14 is a diagram showing a configuration of assembly within the diskarray controller in accordance with the instant invention.

FIG. 15 is a diagram showing another configuration of the inside of adisk array controller in accordance with the invention.

FIG. 16 is a diagram showing another configuration of the inside of adisk array controller in accordance with the invention.

FIG. 17 is a diagram showing a configuration of a disk array controllerin accordance with the invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

Some preferred embodiments of the present invention will be explainedwith reference to the accompanying drawings.

[Embodiment 1]

Referring now to FIG. 1, there is shown one embodiment of thisinvention.

A disk array control device 1 is arranged including two channelinterface (IF) units 11 operatively associated with a host computer 50,two disk IF units 12 associated with a magnetic disk device 20 that hasa group of multiple hard disk drives (HDDs), two selector units 13, twocache memory units 14, two common-use or “shared” memory units 15, anaccess path 0:135, an access path 1:136, and an access path 2:137.

The channel IF unit 11 has two host IFs 102 associated with the hostcomputer 50, two microprocessors 101 for control of input/output withrespect to the host computer 50, a cache memory (CM) access control unit104 for controlling access to the cache memory units 14, and a sharedmemory (SM) access control unit 105 for controlling access to the sharedmemory units 15, and executes data transmission between the hostcomputer 50 and the cache memory units 14 along, with transmission ofcontrol information between the microprocessors 101 and the sharedmemory units 15. The microprocessors 101 and the host IFs 102 areconnected together by an internal bus 106, whereas the CM access controlunit 104 is directly connected to two host IFs 102. The SM accesscontrol unit 105 is directly connected to two microprocessors 101.

The disk IF unit 12 includes two drive IFs 103 associated with themagnetic disk device 20 having HDDs, two microprocessors 101 forcontrolling input/output with respect to the magnetic disk device 20,and a CM access control unit 104 for controlling access to the cachememory unit 14 and an SM access control unit 105 for controlling accessto the shared memory unit 15, and executes data transfer between themagnetic disk device 20 and the cache memory units 14 along withtransmission of control information between the microprocessors 101 andthe shared memory units 15. The microprocessors 101 and drive IFs 103are connected by an internal bus 106 whereas the CM access control unit104 is directly connected to the two drive IFs 103. The SM accesscontrol unit 105 is directly connected to the two microprocessors 101.The disk IF unit also executes RAID functions.

The cache memory unit 14 has a cache memory (CM) controller 107 and amemory module 109, and temporarily stores therein data to be recorded onthe magnetic disk device 20.

The shared memory unit 15 has a shared memory (SM) controller 108 and amemory module 109, for storing control information of the disk arraycontroller 1 (for example, information as to data transfer controlbetween the channel IF units and disk IF units and the cache memoryunits 14) and the like.

The two lines of access paths 0:135 are connected to the CM accesscontrol unit 104 and further connected to two different selector units13 respectively. The two lines of access paths 1:136 are connected tothe selector units 13 and further connected to two different CMcontrollers 107 respectively. Accordingly, two access paths 1:136 intotal, one of which is from one of the two selector units and the otherof which is from the remaining selector unit, are connected to the CMcontroller 107. With such an arrangement, two access routes areestablished from a single CM access control unit 104 toward a single CMcontroller 107. Thus, it becomes possible even where disturbance ortrouble occurs at either an access path or selector unit 13 to getaccess to the cache memory units 14 by use of the remaining one of theaccess routes, which in turn makes it possible to improve the robustnessagainst obstruction, also known as fault tolerance.

The two lines of access paths 2:137 are connected to the SM accesscontrol unit 105 and further connected to two different SM controllersrespectively. Accordingly, there are connected to the SM controller 108four lines of access paths 2:137 in total, which are selected on aone-per-IF basis-i.e. two of them are from two channel IF units 11respectively while the other two are from two disk IF units 12respectively. Although in this embodiment a single access path 2:137 wasconnected between a single SM access control unit 105 and a single SMcontroller 108, increasing this access path 2:137 up to two linesresults in establishment of two access routes from one SM access controlunit 105 to one SM controller 108, which in turn enables improvement ofthe robustness against operation failures (fault tolerance).

Connected to the selector unit 13 are the total 10 number of four linesof access paths 0:135 as selected on a one-per-IF basis-namely, two ofthem are from the two channel IF units 11 respectively whereas theremaining two are from the two disk IF units 12 respectively.Additionally, the selector unit 13 is associated with two lines in totalof access paths 1:136 as connected thereto, each of which is toward oneof the two cache memory units 14.

As the above-stated path-number relationship is established between theaccess path 0:135) and access path 1:136, the selector unit 13 has afunction of selecting for execution only two from among those requestsfrom four lines of access paths 0:135 from the channel IF units 11 anddisk IF units 12, which correspond to the number of the access paths1:136 toward the cache memory units 14.

One significant feature of this embodiment lies in that the connectionform between the channel and disk IF units 11, 12 and the cache memoryunits 14 is different from the connection form between the channel anddisk IF units 11, 12 and the shared memory units 15. The reason for useof such configuration will be explained in conjunction with FIGS. 1-2.

With a disk array control device 2 of the star connection form shown inFIG. 2, in the case of increasing the number of either the channel IFunits 11 or disk IF units 12 as built in the disk array controller 2,the access buses will likewise increase in number between the channeland disk IF units 11, 12 and the cache memory units 14 and also betweensuch IF units 11, 12 and the shared memory units 15. In addition, in thedisk array controller 2 of star connection form, it is effective inorder to improve the throughput that the access paths increase in numberbetween the channel and disk IF units 11, 12 and the cache memory unit14 and between the channel and disk IF units 11, 12 and the sharedmemory unit 15 to thereby improve the internal path performance orthroughput.

However, the data amount of a single datum to be stored in cache memoryunits 14 is much greater than the data amount of a single controlinformation item being stored in shared memory units 15. One example isthat in a disk control device connected to a mainframe computer, asingle datum to be stored in the cache memory units 14 is approximatelya few kilobytes (e.g. 2 Kbytes) whereas a single control informationitem being stored in the shared memory units 15 is about several bytes(e.g. 4 bytes). Another example is that in a disk control device asconnected to a host computer of open architectures, a single datum to bestored in the cache memory units 14 is about several tens of byte (forexample, 64 bytes) whereas a single control information item beingstored in the shared memory units 15 is about several bytes (e.g. 4bytes). Accordingly, because the amount of data to be transferredbetween the channel and disk IF units 11, 12 and the cache memory units14 is much greater than the data amount being, transferred between thesechannel IF units 11, 12 and the shared memory units 15, it should berequired that the data width of an access path between the channel anddisk IF units 11, 12 and the cache memory units 14 be wider than thedata width of an access path between the same IF units 11, 12 and theshared memory units 15. For instance, the access path of the former isconstituted from a bus of 16-bit width whereas the latter is formed of a4-bit width bus. Due to this, increasing the line number of access pathbetween the channel and disk IF units 11, 12 and the cache memory units14 can result in creation of a problem of either pin number shortage ofan LSI of a cache memory controller within the cache memory unit 14(this cache memory controller is not shown in FIG. 2) or pin numbershortage of a connector at a package for mounting the cache memory units14. Then, in this embodiment, as shown in FIG. 1, the channel IF units11 and disk IF units 12 are connected via the selector units 13 to thecache memory units 14 to thereby reduce the required number of accesspaths as directly connected to the cache memory units 14.

On the other hand, as previously described, the data length of a singlecontrol information item to be stored in the shared memory unit 15 isextremely less than the data length of a single datum being stored inthe cache memory unit 14 so that it is possible for the data width of anaccess path between the channel and disk IF units 11, 12 and the sharedmemory unit 15 to be less than or equal to half of the data width of anaccess path between these IF units 11, 12 and the cache memory unit 14.Consequently, even when increasing the number of paths for access to theshared memory unit 15, there will hardly occur any problems such as pinnumber shortage of the LSI of a shared memory controller (this sharedmemory controller is not illustrated in FIG. 2) within the shared memoryunit.

In addition, in order to shorten a response time to the host computer 50of the disk array controller 1, it is also required to maximally shortenan access time to the control information being stored in the sharedmemory unit 15. However, as done between the CM access control unit 104and CM controller 107 shown in FIG. 1, if the SM access control unit 105and SM controller 108 are connected together via a selector unit then itis no longer possible by overhead of processing tasks at such selectorunit to shorten the access time to the control information as stored inthe shared memory unit 15.

Then, with this embodiment, directly connecting the channel IF units 11and disk IF units 12 to the shared memory units 15 with no selectorunits provided therebetween permits provision of a plurality of accesspaths between the channel and disk IF units 11, 12 and the shared memoryunit 15 to thereby improve the throughput while eliminating processingoverhead events at selector units for minimizing an access time to theshared memory units 15 from the channel IF units 11 and disk IF units12.

It should be noted that although in this embodiment the selector units13 and cache memory units 14 and shared memory units 15 are each doublyconfigured or “duplicated” in a viewpoint of fault toleranceenhancement, the aforementioned effects and advantages are obtainablewithout having to employ such duplexing scheme.

FIG. 4 shows an internal configuration of the 20 CM access control unit104. The CM access control unit 104 has a selector 302, packet buffers303 for temporal storage of an address and command as well as data, apath IF 301 associated with the access path 0:135 as coupled to theselector units 13, data error check units 300, and a data transfercontrol unit 310. Two ports of the selector 302 are connected by datalines 210 to either host IFs 102 or drive IFs 103. The other two portsof the selector 302 are connected to the path IF 301. The path IF 301 isconnected by access paths 0:135 to the selector units 13. The datatransfer control unit 310 is connected by control lines 1:211 to eitherthe host IFs 102 or the drive IFs 103, and is connected by control lines2:212 to data transfer control units 315 within the selector units 13.In addition, the data transfer control unit 310 includes an arbitor 308for performing arbitration of access requests from either the host IF102 or the drive IFs 103 while performing switching of the selector 302.

FIG. 6 shows an internal configuration of the selector unit 13. Theselector unit 13 has four path IFs 301 associated with the access path0:135 connected to the channel IF units 11 and disk IF units 12, twopath IFs 301 associated with the access paths 1:136 connected to the CMcontrollers 107, a selector 306 for connection between the both, packetbutters 303, data error check units 300, an address/command (adr, cmd)decoder 305 for decoding an address and command as sent from the CMaccess control unit(s) 104, and a data transfer control unit 315. Thedata transfer control unit 315 is connected by control lines 2:212 tothe data transfer control units 310 within the CM access control units104 and also is connected by control lines 3:213 to the data transfercontrol units 315 in the CM controllers 107. The data transfer controlunit 315 includes an arbitor 308 for performing arbitration of accessrequests from four access paths 0:135 which were decoded by the adr, cmddecoder 305 while performing switching of the selector 306. The packetbuffers 303 operate in a way such that in cases where a difference indata transfer rate is found between the paths on the side of accesspaths 0:135 and those on the side of access paths 1:136, they exhibitbuffering of part or all of the data being transferred in order toabsorb such rate difference.

The adr, cmd decoder 305 has buffers for storage of an address andcommand, an ad.r extractor unit, and cmd extractor unit (not shown inthe drawing). At the adr, cmd decoder 305, store addresses and/orcommands in buffers as assigned to four access paths 0:135 connected tothe CM access control units 104 on a one-per-path basis-namely, theindividual one of them is assigned to a respective one of four accesspaths 0:135. At the adr extractor unit and cmd extractor unit, specify aCM controller 107 to be accessed ‘and also specify the type or kind ofaccess, and then send to the arbitor 308 within the data transfercontrol unit 135.

FIG. 7 shows a configuration of inside of the cache memory unit 14. Thecache memory unit 14 has a CM controller 107 and memory module 109. TheCM controller 107 has two path IFs 301 associated with the access paths1:136 connected to the selector units 13, a selector 304, packet buffers303 for temporal data storage, data error check units 300, a memorycontrol unit 307 for controlling access to the memory module 109, anadr, cmd decoder 305 for decoding an address and command as sent fromthe CM access control unit(s) 104, and a data transfer control unit 135.The data transfer control unit 315 is connected by control lines 3:213to the data transfer control units 315 within the selector units 13. Thedata transfer control unit 315 uses its arbitor 308 to performarbitration of access requests from two access paths 1:136 as has beendecoded by the adr, cmd decoder 305 while performing switching of theselector 304.

The adr, cmd decoder 305 has buffers, an adr extractor unit, and a cmdextractor unit (now shown in the drawing). At the adr, cmd decoder 305,store addresses and/or commands in buffers that are assigned one-by-oneto two access paths 1:136 as connected to the CM controllers 107. At theadr extractor unit and cmd extractor units, specify the address of amemory to be accessed and the type of access for transmission toward thememory control unit 307. In addition, send access requests from twoaccess paths 1:136 to the arbitor 308 within the data transfer controlunit 315.

A description will next be given of the procedure at the time of gettingaccess to the cache memory units 14. In the event of access to the cachememory unit or units 14, the microprocessor 101 instructs the host IF(s)102 or drive IF(s) 103 to begin access to the cache memory unit(s) 14.

Upon receiving of the instruction of access either the host IF 102 ordrive IF 103 transmits a indicative of such access start via the controleither getting start, signal line(s) 1:211 toward the data transfercontrol unit(s) 310 within the CM access control unit(s) 104.Simultaneously, it sends forth an address, command and data (only whendata writing) through data line(s) 210.

The CM access control unit 104 stores in the packet buffer(s) 303 theaddress and command and data (only when data writing) as sent via thedata line(s) 210. The data transfer control unit 310 performsarbitration to determine the right to use the path IF or IFs 301 forswitching the selector 302.

FIG. 9 shows a flow of access from the CM access control unit 104 to theCM controller 107 in the event of writing data into the cache memoryunit(s) 14. Upon determination of the use right of access path 0:135 15by arbitration, the data transfer control unit 310 within the CM accesscontrol unit 104 generates and issues a signal (REQ) indicative of theaccess start toward the data transfer control unit(s) 315 within theselector unit(s) 13 via the control lines 2:212 (at step 501).Subsequently, send out an address and command (step 502).

Upon receipt of the REQ signal from the CM access control unit 104, thedata transfer control unit 315 within the selector unit 13 next receivesan address and command that will be sent through the access path(s)0:135 to perform arbitration on the basis of an access request asdecoded by the ad.r, cmd decoder 305 (step 503). Once the arbitrationresults in obtainment of the right to connect to the access path(s)1:136, the data transfer control unit 315 switches the selector 306(step 504) while at the same time returning via control line(s) 2:212 tothe data transfer control unit(s) 310 within the CM access controlunit(s) 104 a signal (ACK) indicative 5 of the fact that the right ofconnection to the access path(s) 1:136 has been obtained (step 505).Next, the data transfer control unit 315 outputs via control lines 3:213to the data transfer control unit(s) 315 within the CM controller(s) 107a signal (REQ) indicating the start of access (step 506). Subsequently,send forth an address and command (step 507).

When receiving the ACK signal the CM access control unit 104 reads dataout of the packet buffer(s) 303 for transmission to the access path(s)0:135 through the selector 302 and path IF(s) 301. The selector unit orunits 13 send data transmitted via the access path(s) 0:135 to theaccess path(s) 1:136 through the path(s) IF 301 and selector 306 (step509).

Upon receiving of the REQ signal via the control line(s) 3:213, the datatransfer control unit 315 within the CM controller 107 next receives anaddress and command that will be sent through the access path(s) 1:136to perform arbitration on the basis of the access request that has beendecoded by the adr, cmd decoder 305 (at step 508), thereby switching theselector 304. Store the data as sent via the access path(s) 1:136 in thepacket buffer(s) 303. If the arbitration results in obtainment of theright to give access to the memory module .109 then send memory controlinformation to the memory control unit 307 for effectuation ofpreprocessing for memory access (step 510). Next, read data from thepacket buffer(s) 303 for writing into the memory module 109 via theselector 304 (step 511).

After having completed access to the memory module 109, performpost-processing of such memory’ access and let the data transfer controlunit 315 generate a status (STATUS) indicative of an access situation(step 512). Next, transmit the status to the CM access control unit(s)104 through the selector unit(s) 13 (step 513). Upon receipt of thestatus, the data transfer control unit(s) 315 within the selectorunit(s) 13 turns off the REQ signal to the CM controller(s) 107 (step514). Upon receiving of the status, the data transfer control unit(s)310 within the CM access control unit(s) 104 turns of f the REQ signalto the selector unit(s) 13 (step 515). When having affirmed turn-off ofthe REQ signal from the CM access control unit(s) 104, the data transfercontrol unit(s) 315 within the selector unit(s) 13 turns off the ACKsignal being sent to the CM access control unit(s) 104 (step 516).

Upon receipt of the status, the data transfer control unit 310 withinthe CM access control unit 104 notifies either the host IFs 102 ‘ordrive IFs 103 of termination of access to the cache memory unit(s) 14via control line(s) 1:211.

A flow of access from the CM access control unit(s) 104 to the CMcontroller(s) 107 in the event of reading data out of the cache memoryunit(s) 14 is the same as that in the case of data writing as far as thesteps 501 to 508 and those following the step 512 are concerned.

Here, upon receiving of the ACK signal at step 505, the CM accesscontrol unit 104 enters the data receipt wait state.

When having obtained the memory access right at step 508, the CMcontroller 107 reads data from the memory module 109 for transmission tothe access path(s) 1:136 through the selector(s) 304 and path IF(s) 301.

Upon receipt of data via the access path(s) 1:136, the selector unit orunits 13 send data to the, access path(s) 0:135 through the path IF(s)301 and selector 306.

Upon receiving of data via the access path(s) 0:135, the CM accesscontrol unit 104 transmits data through the selector 302 and data line210 toward either 20 the host IFs 102 or the drive IFs 103.

FIG. 5 shows a configuration inside of the SM access control unit 105.The SM access control unit 105 has a selector 302, packet buffers 303for temporarily storing therein an address and command along with data,a path IF 301 associated with access paths 2:137 connected to the SMcontrollers 108, data error check units 300, and a data transfer controlunit 310. Two ports of the selector 302 are connected by data lines 220to the microprocessors 101. The other two ports of the selector 302 areconnected to the path IF 301. The path IF 301 is connected by accesspaths 2:137 to the SM controllers 108. The data transfer control unit310 is connected by control lines 5:221 to the microprocessors 101 andalso connected by control lines 6:222 to the data transfer control units315 within the SM controllers 108. The data transfer control unit 310uses its arbitor 308 to perform arbitration of access requests from themicroprocessors 101 for switching of the selector 302.

FIG. 8 shows an arrangement inside of the shared memory unit 15. Theshared memory unit 15 has its SM controller 108 and memory module 109.The SM controller 108 has four path IFs 301 associated with the accesspaths 2:137 connected to the SM access control units 105, a selector309, packet buffers 303 for temporal data storage, data error checkunits 300, a memory control unit 307 for controlling access to thememory module 109, an “adr, cmd” decoder 305 for decoding address andcommand as sent from the SM access control unit(s) 105, and a datatransfer control unit 315. The data transfer control unit 315 isconnected by control lines 6:222 to the data transfer control units 310within the SM access control units 105. The data transfer control unit315 performs using its arbitor 308 arbitration of access requests fromfour access paths 2:137 as decoded by the ad.r, cmd decoder 305 forswitching of the selector 309.

The adz-, cmd decoder 305 has buffers, an adr extractor unit, and a cmdextractor unit (not shown). At the adr, cmd decoder 305, store addressand command in certain buffers as assigned to four access paths 2:137connected to the SM controller 108 respectively on a one-to-one basis.At the adr extractor unit and cmd extractor unit, specify the address ofa memory to be accessed along with the type of access for transmissiontoward the memory control unit 307. In addition, it sends accessrequests from four access paths 2:137 to the arbitor 308 within the datatransfer control unit 315.

Next, there will be described a procedure at the time of getting accessto the shared memory units 15. In the case of getting access to theshared memory units 15, the microprocessor 101 sends forth a signalrepresentative of access start through the control lines 5:221 to thedata transfer control unit(s) 310 within the SM access control unit(s)105. Simultaneously, send address and command along with data (only whendata writing) via data lines 220.

The SM access control unit 105 stores in the packet buffer(s) 303 theaddress and command and data (only when data writing) as sent via thedata lines 220. The data transfer control unit 310 performs arbitrationto determine the right to use the path IFs 301 for switching theselector 302.

FIG. 10 shows a flow of access from the SM access control unit 105 tothe SM controller 108 in the case of writing data into the shared memoryunit(s) 15.

Upon determination of the use right of access paths 2:137 by sucharbitration, the data transfer control unit 310 within the SM accesscontrol unit 105 issues a signal 5 (REQ) indicative of access start tothe SM controller 108 via control lines 6:222 (step 601). Then, sendcontinuously address and command along with data (step 602).

Upon receipt of the REQ signal via control line 6:222, the data transfercontrol unit 315 within the SM controller 108 next receives address andcommand and data as sent via the access paths 2:137. Let the adr, cmddecoder 305 decode the address and command; perform arbitration on thebasis of an access request (step 603) for switching the selector 309.Let data be stored in the packet buffer(s) 303. If the arbitrationresults in obtainment of the access right to the memory module 109 thensend memory control information to the memory control unit 307 tothereby perform the preprocessing for memory access (step 604). Next,read data out of the packet buffer(s) 303 for writing into the memorymodule 109 via the selector 309 (step 605).

After having completed an attempt to get access to the memory module109, perform the post-processing of memory access to thereby generate atthe data transfer control unit 315 a status (STATUS) indicative of theaccess situation (step 606). Next, send the status to the SM accesscontrol unit 105 (step 607). Upon receipt of the status, the datatransfer control unit 310 within the SM access control unit 105 turnsoff the REQ signal as sent to the SM controller 108 (step 608).

Upon receiving of the status, the data transfer 5 control unit 310within the SM access control unit 105 notifies via control lines 5:221the microprocessors 101 of termination of access to the shared memoryunits 15.

A flow of access from the SM access control unit 105 to the SMcontroller 108 in the case of reading data from the shared memoryunit(s) 15 is the same as that in the case of data writing with respectto the steps 601 to 604 and the step 606 et seq.

After having performed the preprocessing of memory access at step 604,the SM controller 108 reads data out of the memory module 109 fortransmission to the access paths 2:137 via the selector 309 and pathIF(s) 301.

When receiving data via the access paths 2:137 the SM access controlunit 105 sends data to the microprocessors 101 via the selector 302 anddata lines 220.

It is noted that the disk array controller I of this embodiment, eachchannel IF unit 11 has two built-in host IFs. Each host IF is operableto process those requests from respective channels as connected theretoin a parallel fashion.

Incidentally, the disk array controller 1 is such that in the event ofreading data for transmission to the host computer 50, let data storedin the magnetic disk device 20 be written via the disk IF unit(s) 12into the cache memory unit(s) 14, which data will be read out of thecache memory unit(s) 14 for transmission to the host computer via thechannel IF unit(s) 11. Alternatively, in the case of writing data fromthe host computer 50 into the disk array controller 1, let data sentfrom the host computer 50 to the channel IF unit(s) 12 be written intothe cache memory unit(s) 14, which data will be read from the cachememory unit(s) 14 for writing via the disk IF unit(s) 12 to the magneticdisk device 20. Furthermore, in order to generate a data parity forwriting into the magnetic disk device 20, further access is carried outtwo or three times between the disk IF unit(s) 12 and the cache memoryunit(s) 14. Accordingly, in order to parallel-process all of therequests from respective channels as connected to more than one hostcomputer, it is a must to let the throughput between the channel anddisk IF units 11, 12 and the cache memory units 14 be greater than orequal to twice of the maximum throughput between the host computer 50and the channel IF units 11.

In this embodiment, let both the band width of an access path betweenthe CM access control unit 104 and CM controller 107 and the entirebandwidth between the CM controller 107 and memory module 109 be set ator above twice the maximum bandwidth between the channel IF units 11 andthe host computer 50. Thus, it becomes possible to permit paralleloperation of all the channel IF units 11.

According to this embodiment, it becomes possible to increase thethroughput between the channel and disk IF units 11, 12 and the cachememory units 14 and also increase the throughput between the channel anddisk IF units 11, 12 and the shared memory units 15 while shortening anaccess time required. It is thus possible to provide the intended diskarray controller high in throughput and yet short in response time.Here, as shown in FIG. 15, an interconnection network 140 using switches(SWs) 16 is employed to connect between the channel and disk IF units11, 12 and the cache memory units 14. In this case also, as in thearrangement using the selector units 13 shown in FIG. 1, it becomespossible to enhance the throughput due to an ability to provide aplurality of access paths to the cache memory units 14.

In addition, as shown in FIG. 16, no problems occur in implementation ofthis embodiment even in a disk array controller 1 that is modified toincrease the line number of the access paths 0:135 connected to a singleCM access control unit 104 so that it is twice of that in theconfiguration of FIG. 1, i.e., four lines. It is considered thathigh-speed IFs of 100 MB per second or more in throughput, such as fiberchannels or else, will be used as the host IFs and drive IFs in nearfuture. By taking account of the balance of throughputs at the channelIF units 11 and disk IF units 12, it is required that the throughput ofall the access paths 0:135 connected to a single CM access control unit104 be greater than or equal to the throughput of either all the hostIFs 102 within the channel IF units 11 or all the drive IFs 103 withinthe disk IF units 12. As previously stated, in the case of usinghigh-speed IFs such as fiber channels or else, it is possible byincreasing the line number of access paths 0:135 connected to a singleCM access control unit 104 as shown in FIG. 16 to let the throughput ofaccess paths 0:135 be greater than or equal to the throughput of eitherthe host IF 102 or drive IF 103.

Additionally, although in the disk array controllers of FIGS. 15 and 16the selector units 13 and cache memory units 14 and shared memory units15 are each doubly configured or “duplicated” for fault toleranceenhancement, the effects and advantages above may be obtained withouthaving to employ such duplication.

[Embodiment 2]

In FIG. 1, it becomes possible to increase the reliability of data byduplicating all or part of the memory region between two cache memoryunits 14 to permit writing of the same data into such duplicated tworegions when writing data into the cache memory units 14. A procedure ofwriting data into two cache memory units 14 duplicated is as follows.

The host IF 102 or the drive IF 103 that has received an instruction tostart access sends forth via control lines 1:211 a signal indicative ofthe access start toward the data transfer control unit 310 within the CMaccess control unit 104. Simultaneously, transmit two addresses andcommands along with a single datum through data lines 210.

The CM access control unit 104 stores in its packet buffer(s) 303 thetwo addresses and commands and single datum that have been sent via thedata line(s) 210. The data transfer control unit 310 performsarbitration to determine the use right of the path Ifs 301 for switchingthe selector 302.

FIG. 11 shows a flow of access from the CM 15 access control unit 104 totwo CM controllers a, b: 107 in the case of writing data to two cachememory units 14 duplicated. Upon determining of the use right of accesspaths 0:135 by arbitration, the data transfer control unit 310 withinthe CM access control unit 104 issues via control lines 2:212 a signal(REQ) indicative of the access start to the data transfer control units315 within the selector units 13 (step 701). Subsequently, send twoaddresses and commands progressively (step 702).

Upon receipt of the REQ signal from the CM 25 access control unit 104,the data transfer control unit 315 within the selector unit 13 nextreceives address and command as sent via the access paths 0:135 toperform arbitration on the basis of the access request decoded by theadr, cmd decoder 305 (step 703). If the arbitration results inobtainment of both of the connect rights to two access paths 1:136leading to the CM controllers a, b: 107 then the data transfer controlunit 315 switches the selector 306 (step 704) while at the same timereturning via control lines 2:212 to the data transfer control unit 310within the CM access control unit 104 a signal (ACK) indicative of thefact that the connect rights to the CM controllers a, b:107 have beenobtained (step 705). Next, the data transfer control unit 315 generatesand issues via control lines 3:213 a signal. (REQ) representative of theaccess start toward the data transfer control units 315 within two CMcontrollers 107 (steps 706 a, 706 b). Subsequently, send addresses andcommands one by one to the CM controllers a, b:107. (steps 707 a, 707b).

Upon receiving of the ACK signal, the CM access control unit 104 readsdata out of the packet buffer(s) 303 for transmission via the selector302 and path Ifs 301 toward the access paths 0:135 (step 709). Theselector unit 13 sends a single datum that was sent via the access path0:135 to both of the two access paths 1:136 through the path IFs 301 andselector 306 (step 709 a, 709 b).

Upon receipt of the REQ signal via control line 3:213, the data transfercontrol units 315 within the CM controllers a, b:107 will next receiveaddresses and commands sent over the access paths 1:136 to performarbitration on the basis of the access requests as decoded by the ad.r,cmd decoder 305 (steps 708 a, 708 b) for switching the selector 304. Letthe data sent via the access path(s) 1:136 be stored in the packetbuffer(s) 303. If arbitration results in obtainment of the right to getaccess to the memory module 109 then send memory control information tothe memory control unit 307 and perform the preprocessing for memoryaccess (steps 710 a, 710 b). Next, read data from the packet buffer(s)303 to write into the memory module 109 via the selector 304 (step 711a, 711 b).

Upon completion of access to the memory module 109, performpost-processing of memory access; then, let the data transfer controlunit 315 generate a status (STATUS) indicative of such access situation(steps 712 a, 712 b). Next, send the status via the selector unit 13 tothe CM access control units 104 (steps 713 a, 713 b). Upon receiving ofthe status, the data transfer control unit 315 within the selector unit13 turns off respective REQ signals as sent to the CM controllers a,b:107 (steps 714 a, 174 b). In addition, when receiving the statusesfrom both of the CM controllers a, b: 107, the selector unit 13 sendsthem to the CM access control unit(s) 104 in succession (step 713). Uponreceipt of two statuses, the data transfer control unit 310 within theCM access control unit 104 turns off the REQ signal being sent to theselector unit 13 (step 715). Once the turn-off of the REQ signal fromthe CM access control unit 104 is affirmed, the data transfer controlunit 315 within the selector unit 13 turns off the ACK signal as sent tothe CM access control unit 104 (step 716).

Upon receipt of the status, the data transfer 5 control unit 310 withinthe CM access control unit 104 notifies via control lines 1:211 eitherthe host IFs 102 or the drive IFs 103 of termination of access to thecache memory units 14.

As previously stated, in the case of doubly 10 writing data into theduplicated cache memory units 14, it is required, while one of the dataitems to be doubly written is being subject to the write processing, toprevent unintentional rewriting of the remaining one of the data itemsin deference to a write request from the other access path. In thisembodiment, let a directory of the cache memory unit(s) 14 be stored inthe shared memory unit(s) 15 to thereby assure establishment of a bitindicative of busy-to-access in the directory as stored in the sharedmemory unit(s) 15 prior to getting access to the cache memory units 14without exceptions. With such an arrangement, because only one accessrequest is issued for the same address within the cache memory units 14at the same time, it is possible during effectuation of write processingof one datum of the data being doubly written to prevent unintentionalrewriting of the other datum in reply to a write request from theremaining access path.

[Embodiment 3]

With the disk array controller 1, in case a plurality of cache memoryunits 14 are provided, there should be required a function of copyingdata from a certain cache memory unit 14 to another cache memory unit14. This function is achievable by a procedure as will be describedbelow.

The host IF 102 or the drive IF 103 that has received the instruction tostart getting access sends out via control lines 1:211 a signalindicative of the access start to the data transfer control unit 310 inthe CM access control unit 104. Simultaneously, transmit two addressesand commands through data lines 210. One address and command of the twomay be an address of the copy source and a read command whereas anotheraddress and command might be an address of a copy destination or targetand a write command. Here, an explanation will be given under anassumption that the CM controllers a: 107 is the copy source whereas theCM controller b:107 is the target.

The CM access control unit 104 stores in its packet buffer(s) 303 twoaddress and commands that have been sent via data lines 210. The datatransfer control unit 310 performs arbitration to determine the right touse the path IFs 301 for switching the selector 302. FIG. 12 shows aflow of access from the CM access control unit 104 to the CM controllersa, b:107 in the event of copying data between two cache memory units.Upon determination of the use right of access paths 0:135 througharbitration, the data transfer control unit 310 within the CM accesscontrol unit 104 issues via control lines 2:212 a signal (REQ)indicative of access start toward the data transfer control units 315within the selector units 13 (step 801). Subsequently, it sends out twoaddresses and commands consecutively (step 802).

Upon receipt of the REQ signal from the CM access control unit 104, thedata transfer control unit 315 within the selector unit 13 will nextreceive address and command as sent via the access path(s) 0:135 toperform arbitration on the basis of the access request decoded by theadr, cmd decoder 305 (step 803). If the arbitration results inobtainment of both of the connect rights to two access paths 1:136leading to the CM controllers a, b:107 then the data transfer controlunit 315 switches the selector 306 (step 804) while simultaneouslyreturning via control lines 2:212 to the data transfer control unit 310within the CM access control unit 104 a signal (ACK) indicative of thefact that the right to connect to both of the CM controllers a, b: 107has been obtained (step 805). Next, the data transfer control unit 315outputs via control lines 3:213 a signal (REQ) indicative of accessstart to the data transfer control units 315 within the CM controllersa, b:107 (steps 806 a, 806 b). Subsequently, send respective addressesand commands to the CM controllers a, b: 107 (steps 807 a, 807 b).

Upon receiving of the ACK signal, the CM access control unit 104 entersa state waiting for receipt of a status that notifies the termination ofaccess event.

When receiving the REQ signal via the control lines 3:213, the datatransfer control unit 315 within the CM controller a:107 of the copysource will next receive address and command sent through the accesspath 1:136 to perform arbitration on the basis of the access request asdecoded by the adr, cmd decoder 305 (step 808) for switching theselector 304. If such arbitration results in obtainment of the right toget access to the memory module 109 then send memory control informationto the memory control unit 307 and then’ perform preprocessing formemory access (step 809). Next, read data from the memory module 109(step 810) for transmission via the selector 304 to access path 1:136(step 811 a).

The selector unit 13 sends the data, which was sent via access path1:136 from the CM controller a:107, toward the access path 1:136connected to the CM controller b (step 811 b).

Upon receipt of the REQ signal via control line(s) 3:213, the datatransfer control unit 315 within the CM controller b:107 will nextreceive address and command sent through the access path 1:136 fordecoding at the adr, cmd decoder 305. Thereafter, wait for initiation ofdata reception; then, participate in arbitration of memory access (step812). Let the data sent via the access path 1:136 be stored in thepacket buffer(s) 303. If the arbitration results in obtainment of theright to get access to the memory module 109 then send memory controlinformation to the memory control unit 307 and perform preprocessing formemory access (step 813). Next, read data out of the packet buffer(s)303 for writing into the memory module 109 via the selector 304 (step814).

Upon completion of access to respective CM 10 memory modules 109, the CMcontrollers a, b: 107 perform post-processing of memory access forgeneration of statuses (STATUS) indicative of the access situation attheir data transfer control units 315 (steps 815, 818). Next, send thestatuses to the selector units 13 (steps 816, 819).

Upon receiving of the statuses, the data transfer control unit 315within the selector unit 13 turns off respective REQ signals for the CMcontrollers a, b: 107 (steps 817, 821). In addition, when receivingstatuses from both of two CM controllers a, b:107, the selector unit 13sequentially sends them to the CM access control unit (step 820). Uponreceipt of two statuses, the data transfer control unit 310 within theCM access control unit 104 turns off the REQ signal for the selectorunit 13 (step 822). When affirming turn-off of the’ REQ signal from theCM access control unit 104, the data transfer control unit 315 withinthe selector unit 13 turns off an ACK signal for the CM access controlunit 104 (step 823).

Upon receiving of the status, the data transfer control unit 310 withinthe CM access control unit 104 notifies via control line(s) 1:211 eitherthe hosts IF 102 or drive IFs 103 of the termination of access to thecache memory units 14.

In the disk array controller 1, there is also required a function ofcopying data from a certain address to another address within a singlecache memory unit 14.

This function is achievable, in the data write procedure shown in FIG.9, instead of the write access to the memory module 109 at step 511, byreading data from the memory module 109 for storage in the packetbuffer(s) 303 within the CM controller 107 and then continuously writingsuch data into the memory module 109.

[Embodiment 4]

In FIG. 1, it becomes possible to increase the reliability of data byduplicating the whole or part of the memory region between two sharedmemory units 15 for permitting writing of the same data in such twoduplicated regions when writing data into the shared memory units 15.

A procedure in the case of writing data into 25 the two shared memoryunits 15 duplicated is as follows.

The microprocessor 101 sends out a specific signal via control line5:221 to the data transfer control unit 310 within the SM access controlunit 105, which signal indicates access start. Simultaneously, send twoaddresses and commands along with a single data item through dataline(s) 220.

The SM access control unit 105 stores in its packet buffer(s) 303 thetwo addresses and commands and a single data item as sent via the datalines 220. The data transfer control unit 310 performs arbitration todetermine the use right of the paths IF 301 for switching the selector302.

FIG. 13 shows a flow of access from the SM access control unit 105 totwo SM controllers 108 in the case of writing data into two sharedmemory units 15 duplicated. In case two shared memory units 15 areduplicated, one of them is set as a master whereas the other is as aslave. The data transfer control unit 310 within the SM access controlunit 105 first determines through arbitration the use right of accesspath 2:137 leading to a maser-side SM controller ‘108 and then issuesvia control line 6:222 a signal (REQ) indicative of access start towardthe data transfer control unit 315 within the master-side SM controller108 (step 901). Then, send address and command and data successively(step 902).

Upon receipt of the REQ signal via the control line 6:222, the datatransfer control unit 315 within the master-side SM controller 108 willnext receive address, command and data sent via access path(s) 2:137 toperform arbitration on the basis of an access request as decoded by theadr, cmd decoder 305 (step 903), and then switches the selector 309. Letdata be stored in the packet buffer(s) 303. If the arbitration resultsin obtainment of the right to get access to the memory module 109 thensend memory control information to the memory control unit 307 andperform preprocessing for memory access (step 904). Next, read data outof the packet buffer(s) 303 for writing into the memory module 109 viathe selector 309 (step 905).

Upon completion of access to the memory module 109, performpost-processing of memory access for generation of a status (STATUS) atthe data transfer control unit 315 (step 906). Next, send the status tothe SM access control unit 105 (step 907). Upon receiving of the status,the SM access control unit 105 determines through arbitration the useright of the access path 2:137 leading to the slave-side SM controller108 while eliminating release of the use right of access path 2:137leading to the master-side SM controller 108. The following accessprocedure (steps 908-914) to the slave-side SM controller 108 is thesame as the access procedure (steps 901-907) to the master-side SMcontroller 108.

Upon receipt of the status from the slave-side SM controller 108, thedata transfer control unit 310 within the SM access control unit 105turns off the REQ signals for both of the master-side and slave-side SMcontrollers 108 (steps 715 a, 715 b).

In the case of doubly writing or “duplicating” data into the duplicatedshared memory units 15, the shared memory units 15 are divided into themaster and slave in the way stated above to thereby write data thereintoin the order of sequence that the master side is first and the slaveside follows, and the both access paths 2:137 are not released untilcompletion of data writing to the slave side. Whereby, the data writesequence is guaranteed, which in turn makes it possible to prevent,during performing writing of one datum of the data to be doubly written,any unintentional rewriting of the other datum in response to a writerequest from another access path.

Upon receiving of the status the data transfer control unit 310 withinthe SM access control unit 105 notifies via control line 5:221 themicroprocessor 101 of the termination of, access to the shared memoryunits 15.

[Embodiment 5]

Referring to FIG. 14, there is shown a configuration for use in assemblyof the channel IF units 11, disk IF ‘units 12, selector units 13, cachememory units 14 and shared memory units 15 of the disk array controller1 of the embodiment 1.

The channel IF units 11, disk IF units 12, selector units 13, cachememory units 14 and shared memory units 15 are mounted or “sealed” inindependent packages (PKs) respectively-that is, channel IF PKs 1, diskIF PKs 2, selector PKs 3, and memory PKs 4. Let different cache memoryunits 14 be mounted on different packages. Similarly, let differentshared memory units 15 be on different packages. No specific problemswould occur even when one cache memory unit 14 and one shared memoryunit 15 are mounted on the same package. In FIG. 14, there is shown anexample with one cache memory unit 14 and one shared memory unit 15mounted or sealed in the same package PK 4.

Let the channel IF PKs 1, disk IF PKs 2, selector PKs 3 and memory PKs 4be mounted on a platter 5, which in turn is built in a housing orenclosure.

In this embodiment the selector units 13 are arranged so that these aremounted on the selector PK5 3 to be laid out on the opposite peripheralsides of the platter 5. However, there are no problems even when theyare not mounted on any packages and instead are directly mounted on theboth sides of the platter.

[Embodiment 6]

As shown in FIG. 17, unlike the disk array controller 1 of theembodiment 1 shown in FIG. 1 with the access path 2:137 used to connectbetween the SM access control unit 105 and SM controller 108, two sharedbuses 130 are employed to connect therebetween. As per FIG. 17, providedfrom the SM access control unit 105 are connection paths each of whichis for one of the two shared buses 130. Also provided from the SMcontroller 108 are connection paths, each for one of the two sharedbuses 130. The SM access control unit 105 and SM controller 108 haveeach two arbitors. Two arbitors are the arbitors for use in performingarbitration of two shared buses, respectively. When getting access tothe SM controller 108 from the SM access control unit 105, one of aplurality of arbitors becomes the master for use in performingarbitration of the use right of shared bus 130. The SM access controlunit 105 that has obtained the use right gets access to the SMcontroller 108. Optionally, in the alternative of providing sucharbitors inside of the SM access control unit 105 and SM controller 108,these may be directly connected as independent circuitry to the sharedbuses 130 without suffering from any specific problems. With the sharedbus connection, widening the data width of buses makes it possible toincrease data transfer rate, which in turn enables shortening of a timetaken to give access to the shared memory units 15.

As has been described above, since the data width of the access path2:137 in FIG. 1 can be made smaller than the data width of the accesspath 0:135 by twice or more, even when the star connection (one-to-oneconnection) is employed to connect between the channel IF units 11 anddisk IF units 12 and the shared memory units 15 as shown in FIG. 1,problems will hardly occur as to the pin neck of an LSI for assembly ofthe shared memory units. Even in view of this, there still remains thepossibility that an excessive increase in line number of access path2:137 can result in creation of a problem that it is no longer possibleto mount such access path 2:137. If this is the case, the shared busconnection of this embodiment will become effective.

It should be noted that although in this embodiment the selector unit 13and cache memory unit 14 and shared memory unit 14 are each ofduplicated configuration, the aforesaid effects are obtainable withoutuse of such duplicated configuration. According to the presentinvention, with regard to the access paths between the channel and diskIF units and cache memory, it is possible to make the throughput high.In addition, regarding the access paths between the channel and disk IFunits and shared memory, the throughput can be made higher whileshortening the access time. Thus, it becomes possible to provide thedisk array control device that is high in throughput and yet short inresponse time.

What is claimed is:
 1. A disk array control device comprising: at leastone channel interface unit having an interface with a host computer; atleast one disk interface unit having an interface with a magnetic diskdevice; at least one cache memory unit; at least one shared memory unit;at least one selector provided between said at least one channelinterface unit, said at least one disk interface unit and said at leastone cache memory, where said selector selectively connects said at leastone cache memory unit, said at least one channel interface unit and saidat least one disk interface unit; a channel interface package in whichsaid channel interface is mounted; a disk interface package in whichsaid disk interface unit is mounted; a memory package in which saidcache memory or shared memory is mounted; a selector package in whichsaid at least one selector is mounted; a backplane upon which saidchannel interface package, said disk interface package, said memorypackage and said selector package are mounted, wherein said selectorpackage is arranged to be disposed at a position outside of a center ofsaid backplane.
 2. A disk array control device according to claim 1,wherein said at least one selector is arranged to be disposed at aposition more peripheral with respect to said packages.
 3. A disk arraycontrol device comprising: first means for providing an interface with ahost computer; second means for providing an interface with a magneticdisk drive; third means for providing a cache memory; fourth means forproviding a shared memory; fifth means for selectively connecting saidfirst and second means to said third and fourth means; sixth means forsealing said first means; seventh means for sealing said second means;eight means for sealing said third means; ninth means for sealing saidfifth means; and tenth means for providing a platform in which saidsixth, seventh, eighth and ninth means are mounted, wherein said ninthmeans is arranged to be disposed at a position outside of a center ofsaid tenth means.
 4. A disk array control device comprising: a pluralityof channel interface units having an interface with a host computer; aplurality of disk interface units having an interface with a magneticdisk device; a plurality of cache memory units; a plurality of selectorsselectively connectable to said plurality of channel interface units,said plurality of disk interface units and said plurality of cachememory units; a channel interface package in which said plurality ofchannel interface units are mounted; a disk interface package in whichsaid plurality of disk interface units are mounted; a memory package inwhich said plurality of cache memory units are mounted; a plurality ofselector packages in which one of said plurality of selectors ismounted; and a platter upon which said channel interface package, saiddisk interface package, said memory package and said plurality ofselector packages are mounted, wherein said plurality of selectors sendsa command received from one of said plurality of channel interfaceunits, said plurality of disk interface units, and said plurality ofcache memory units to the another one of said plurality of channelinterface units, said plurality of disk interface units, and saidplurality of cache memory units, wherein said plurality of selectorpackages is mounted upon a peripheral side of said platter.
 5. A diskarray control device according to claim 4, wherein said plurality ofselector packages are mounted at each side of the platter.
 6. A diskarray control device according to claim 5, wherein one of said pluralityof selectors is sealed in one of said plurality of selector packages. 7.A disk array control device comprising: a plurality of channel interfaceunits having an interface with a host computer; a plurality of diskinterface units having an interface with a magnetic disk device; aplurality of cache memory units; a plurality of selectors selectivelyconnectable to said a plurality of channel interface units, said aplurality of disk interface units and said a plurality of cache memoryunits; a channel interface package in which said plurality of channelinterface units are mounted; a disk interface package in which saidplurality of disk interface units are mounted; a memory package in whichsaid plurality of cache memory units are mounted; a plurality ofselector packages in which one of said plurality of selector is mounted;and a platter upon which said channel interface package, said diskinterface package, said memory package and said plurality of selectorpackages are mounted, wherein said plurality of selectors sends acommand received from one of said plurality of channel interface units,said plurality of disk interface units, and said plurality of cachememory units to the another one of said plurality of channel interfaceunits, said plurality of disk interface units, and said plurality ofcache memory units, and wherein said plurality of selector packages ismounted upon the edge of said platter.
 8. A disk array comprising: aplurality of magnetic disk device; and a disk array control device,wherein said disk array control device comprises: a plurality of channelinterface units having an interface connectable to a host computer, aplurality of disk interface units having an interface connectable tosaid plurality of magnetic disk device, a plurality of cache memoryunits, a plurality of selectors selectively connectable to saidplurality of channel interface units, said a plurality of disk interfaceunits and said a plurality of cache memory units; a channel interfacepackage in which said plurality of channel interface units are mounted,a disk interface package in which said plurality of cache memory unitsare mounted, a plurality of selector packages in which one of saidplurality of selector is mounted, and a platter upon which said channelinterface package, said disk interface package, said memory package andsaid plurality of selector packages are mounted, wherein said pluralityof selectors sends a command received from one of said plurality ofchannel interface units, said plurality of disk interface units, andsaid plurality of cache memory units to another one of said plurality ofchannel interface units, said plurality of disk interface units, andsaid plurality of cache memory units, and wherein said plurality ofselector packages is mounted upon the peripheral side of said platter.